Powdered crosslinked polymers containing carboxyl groups (hereinafter sometimes referred to as crosslinked polymers) are characterized in that they dissolve in water and exhibit extremely high viscosity even in low concentrations by neutralizing them with appropriate bases and form plastic fluid with a high yield value. They have been used in various fields on the basis of these special flowing properties. For example, they have been used in the industrial fields as solid suspension stabilizers (e.g., gypsum, cement, etc.), thickeners (e.g., water-soluble paint, emulsion paint, etc.), pastes (e.g., printing paste in the textile industry, etc.); in the field of cosmetics and toiletries in cream, lotion, shampoo, dentifrice on the basis of thickening and suspension stabilizing properties; and in the pharmaceutical field in ointments, tablets or the like.
Such crosslinked polymers have been produced by known methods, for example, by copolymerization of an .alpha.,.beta.-unsaturated carboxylic acid such as acrylic acid and a monomer having at least two ethylenic unsaturated groups such as polyallyl ether of sucrose (U.S. Pat. No. 2,923,692), hexaallyltrimethylene trisulfone (U.S. Pat. No. 2,958,679), triallyl phosphate (U.S. Pat. No. 3,426,004) or the like; or by copolymerization of an .alpha.,.beta.-unsaturated carboxylic acid such as acrylic acid and a polymerizable monomer having a glycidyl group such as glycidyl methacrylate (JP-A 58-84819) or the like, followed by heating. The crosslinked polymers obtained by these prior art methods do not have satisfactory properties.
On the other hand, when these crosslinked polymers are used as a thickener for various solutions, the higher the viscosity the crosslinked polymers exhibit, the more various uses they have. Further, desired thickening effects can be obtained even by using a smaller amount of them. The crosslinked polymers thus have high value as goods.